The present invention concerns the art of PBZ polymers and in particular branched compositions containing those polymers.
PBZ polymers (see definition for PBZ polymers herein) are commonly known as polybenzoxazoles, polybenzothiazoles and polybenzimidazoles. PBZ polymers and their synthesis are described in detail in the following patents and article, the teachings of which are incorporated herein by reference: Wolfe et al., Liquid Crystalline Polymer Compositions, Process and Products, U.S. Pat. No. 4,703,103 (Oct. 27, 1987); Wolfe et al., Liquid Crystalline Polymer Compositions, Process and Products, U.S. Pat. No. 4,533,692 (Aug. 6, 1985); Wolfe et al., Liquid Crystalline Poly(2,6- Benzothiazole) Compositions Process and Products, U.S. Pat. No. 4,533,724 (Aug. 6, 1985); Wolfe et al., Liquid Crystalline Polymer Compositions, Process and Products, U.S. Pat. No. 4,533,693 (Aug. 6, 1985); Evers, Thermooxidatively Stable Articulated P-Benzobisoxazole and P-Benzobisthiazole Polymers, U.S. Pat. No. 4,359,567 (Nov. 16, 1982); Tsai et al., Method for Making Heterocyclic Block Copolymers, U.S. Pat. No. 4,578,432 (Mar. 25, 1986); and "Polybenzothiazoles and Polybenzoxazoles", 11 Ency. Poly. Sci. & Eng., 601-635 (J. Wiley & Sons, Inc. 1988).
PBZ polymers have generated considerable research interest due to their unique physical properties. PBZ polymers can exhibit remarkable high-temperature stability, high tensile strength and high tensile modulus. PBZ polymers are resistant to harsh environments and, therefore, useful for military, aerospace, automotive, and other applications requiring high performance materials.
Due to their unique thermal and environmental stability, PBZ polymers can be difficult to fabricate into useful articles of manufacture, especially where the PBZ polymer is a rigid-rod PBZ polymer, Rigid-rod PBZ polymers are those polymers which consist of essentially rectilinear polymer structures. In general, useful articles are made from both rigid-rid and non-rigid-rod PBZ polymers by dissolving them in a suitable solvent, typically polyphosphoric acid, to form either anisotropic liquid crystalline compositions or isotropic compositions, the nature of the resulting composition depending upon the PBZ polymer in question and its concentration. These compositions can be processed by known methods to form fibers and films. The fibers can be incorporated as a reinforcing agent within a thermosetting polymer, such as an epoxy resin, to form a composite that can be converted into strong, light articles of manufacture.